The invention relates to a closed-cell, non-crosslinked polyethylene foam structure of relatively small cell size and relatively low cross-section minor to major dimension ratio. The extruded structure is substantially free of distortion, convolution, or corrugation from its intended shape or geometry.
Solid closed-cell polyethylene foam structures of relatively low cross-section minor to major dimension ratio, height to width in the case of those of rectangular cross-section, have found numerous commercial applications such as cushioning, packaging, insulation, sheeting, and the like. To enhance insulative performance, softness, sound absorption, and nonabrasiveness of such structures, it would be desirable to reduce the cell size of the polyethylene foam comprising the structure.
A problem with making solid closed-cell, non-crosslinked polyethylene foam structures of relatively small cell sizes (e.g. 0.02 to 0.5 mm) and relatively low cross-section dimension ratios (e.g. 1/8 or less) is that the structure actually formed may be in a geometry or shape other than that intended. As the foamable composition from which the structure is made exits the die, it is not able to expand directionally outward with respect to the major dimension of the die orifice at a rate sufficient to prevent the structure from becoming distorted, convoluted, or corrugated along its major dimension. The structure cannot expand rapidly enough because relatively small cell size foams have relatively high foaming rates, which result from the relatively high levels of nucleator required to make foams having relatively small cell size.
It would be desirable to have a closed-cell, non-crosslinked polyethylene foam structure of relatively low cross-section minor to major dimension ratio comprised of a polyethylene foam of relatively small cell size. Such foam structure would be substantially free of deviation or distortion from its intended shape or geometry.